nanoantennas for visible and infrared radiation
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Nanoantennas for visible and infrared radiation
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2012 Rep. Prog. Phys. 75 024402
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IOP PUBLISHING REPORTS ON PROGRESS IN PHYSICS
Rep. Prog. Phys. 75 (2012) 024402 (40pp) doi:10.1088/0034-4885/75/2/024402
Nanoantennas for visible and infraredradiationPaolo Biagioni1, Jer-Shing Huang2 and Bert Hecht31 CNISMDipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano,Italy2 Department of Chemistry and Frontier Research Center on Fundamental and Applied Science ofMatters, National Tsing Hua University, Hsinchu 30013, Taiwan3 Nano-Optics & Biophotonics Group, Department of Experimental Physics 5, Wilhelm Conrad RontgenResearch Center for Complex Material Systems (RCCM), Physics Institute, University of Wurzburg, AmHubland, D-97074 Wurzburg, Germany
Received 10 May 2011, in final form 26 August 2011Published 27 January 2012Online at stacks.iop.org/RoPP/75/024402
AbstractNanoantennas for visible and infrared radiation can strongly enhance the interaction of lightwith nanoscale matter by their ability to efficiently link propagating and spatially localizedoptical fields. This ability unlocks an enormous potential for applications ranging fromnanoscale optical microscopy and spectroscopy over solar energy conversion, integratedoptical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing aswell as enhancement of optical nonlinearities. Here we review the current understanding ofmetallic optical antennas based on the background of both well-developed radiowave antennaengineering and plasmonics. In particular, we discuss the role of plasmonic resonances on theperformance of nanoantennas and address the influence of geometrical parameters imposed bynanofabrication. Finally, we give a brief account of the current status of the field and the majorestablished and emerging lines of investigation in this vivid area of research.
(Some figures may appear in colour only in the online journal)This article was invited by J Weiner.
1. Introduction 21.1. Antenna basics: radiation and near field of a
time-dependent charge distribution 21.2. Towards optical antennas: from perfect metals
to plasmonic materials 31.3. Potential of nanoantennas at optical frequencies 31.4. Outline 4
2. Elements of classical antenna theory 52.1. Introduction to antenna language 52.2. Reciprocity theorem 62.3. What radio-frequency-antenna engineers may
be concerned with 73. Properties of metals at optical frequencies 8
3.1. DrudeSommerfeld model 83.2. Interband transitions 83.3. Comparison of relevant metals 8
4. Properties of isolated optical antennas 94.1. Single-particle plasmon resonances 94.2. Resonances of two-wire antennas 124.3. A case study of single- and two-wire antennas
by simulations 134.4. Radiation patterns of plasmonic linear antennas 15
5. Elements of optical antenna theory 155.1. Nanoantennas driven by quantum emitters 155.2. Lumped elements at optical frequencies 175.3. What optical antenna engineers may be
concerned with 206. On the defining properties of optical antennas 207. Fabrication of nanoantennas 21
7.1. Electron-beam lithography 217.2. Focused ion-beam milling 227.3. Nano-imprint lithography 22
0034-4885/12/024402+40$88.00 1 2012 IOP Publishing Ltd Printed in the UK & the USA
Rep. Prog. Phys. 75 (2012) 024402 P Biagioni et al
7.4. Self- and atomic-force-microscopy-basedassembly of nanoantennas 22
7.5. Nanoantennas on tips 237.6. Fundamental material issues 23
8. Experimentally studied geometries of metal opticalantennas 248.1. Single nanospheres and nanorods 248.2. Nanosphere and nanorod dimers 248.3. Bow-tie nanoantennas 248.4. YagiUda nanoantennas 248.5. Other nanoantenna geometries 258.6. Substrate effects 26
9. Characterization of nanoantennas 269.1. Elastic and inelastic light scattering 269.2. Near-field intensity distribution 279.3. Emission patterns 289.4. Spectral properties 28
10. Applications and perspectives of nanoantennas 2910.1. Scanning near-field optical microscopy,
spectroscopy and lithography 2910.2. Nanoantenna-based single-photon superemitters 2910.3. Optical tweezing with nanoantennas 3010.4. Antenna-based photovoltaics and infrared
detection 3010.5. Optical antenna sensors 3010.6. Ultrafast and nonlinear optics with
nanoantennas 3110.7. Perspectives for lasing in nanoantennas 3110.8. Nanoantennas and plasmonic circuits 3210.9. Nanoantennas and thermal fields 32
11. Conclusions 32Acknowledgments 33References 33
In 1959, when nanoscience as we know it today was stillfar from being a reality, Richard Feynman gave a talk at theannual meeting of the American Physical Society, entitledTheres plenty of room at the bottom . In this talkFeynman anticipated most of the experimental fields and issuesof concern which, more than 20 years later, would become keyissues in the understanding of phenomena on the nanometerscale. While talking about the possibility of building nanoscaleelectric circuits, he also posed the question: ...is it possible,for example, to emit light from a whole set of antennas, like weemit radio waves from an organized set of antennas to beam theradio programs to Europe? The same thing would be to beamthe light out in a definite direction with very high intensity....Today, we can safely state that Feynmans suggestion hasalready become reality and research on nanoantennas that workat optical frequencies has developed into a strong branch ofnanosciencenano-optics in particularwith many excitingperspectives. It is the goal of this report to summarize andexplain the current understanding of optical antennas on thebackground of both the highly developed field of antennaengineering [2, 3] and of plasmonics .
Although Feynmans work was right before the eyes ofeverybody for a long time, it took the solid development ofnear-field optics  to acquire enough proficiency in usingnanostructures to influence the flow of light at deep sub-wavelength scales with the required precision. Althoughit is not the intention of this report to provide a detailedaccount of the chronological development of the field, wenevertheless would like to mention a few selected publicationsthat inspired the authors to enter into the field of nanoantennas.First of all there is the visionary book chapter by DieterW Pohl , in which he points out the similarities betweenfluorescing molecules, small scattering particles, etc, andtelecommunication antennas and suggests to inspect antennatheory for concepts applicable and useful to near-field optics.Another eye opener was the paper by Grober et al , inwhich the authors explicitly discuss the use of nanoantennas
for scanning near-field optical microscopy and provide proof-of-principle experiments using microwave radiationan idealater on brought close to realization by Oesterschulze et al .Many other efforts dealing with antenna-like structures dateback to the 1980s and even before, mostly driven by the needfor efficient infrared (IR) detectors. A good account is givenin recent reviews [11, 12].
1.1. Antenna basics: radiation and near field of atime-dependent charge distribution
Antennas are used either to create electromagnetic (EM)waves with a well-defined radiation pattern, which can thentravel over large distances, or to receive EM waves from aremote source in order to extract some encoded information, tomeasure changes in their intensity, or to exploit the transmittedpower . Today the importance of antennas is dominatedby their ability to provide an interface between localizedinformation processing using electrical signals and the free-space wireless transmission of information encoded in variousparameters of EM waves, such as amplitude, phase andfrequency. Due to these properties, antennas and EM radiationhave become indispensable assets to science and technologyas well as to our everyday life.
The function of an antenna is based on the fact thatfree charge carriers are constricted into certain well-definedregions of space. These charges may start to oscillate if anac voltage is applied or an EM wave is reaching such a region.Examples for such systems are the conduction electrons inpieces of metal [2, 3] as well as electrons and ions in a gasdischarge tube . An ac voltage applied to a piece of metalchanges the spatial distribution of charges as a function oftime, which in turn will eventually affect the electric fieldof the charge distribution at any distance from the source.Due to the finite speed of light c, any change in the chargedistribution that occurs at time to results in a change in theelectric field at a remote point at a distance R only after a timeto + (nR/c), where n is the refractive index of the medium.
Rep. Prog. Phys. 75 (2012) 024402 P Biagioni et al
A well-known fundamental source of such EM disturbancesis a harmonically oscillating dipole which may be pictured astwo metallic spheres connected by a thin wire as it was realizedin H Hertzs pioneering experiments . If such a systemis prepared in an initial state where some negative charge ison one sphere and the corresponding positive charge on theother one, the systemwhen left alonewill start to performan exponentially damped